Many industrial operations generate malodorous and/or toxic gases which, in years gone by, have merely been exhausted to the atmosphere. Such pollution of the atmosphere is no longer permitted and it is necessary to remove or otherwise render innocuous the gaseous pollutants. Although, in recognition of the frequently inordinate expense of completely removing such pollutants, it is permissible to discharge air containing less than officially specified minimal amounts of such pollutants to the atmosphere, it is nevertheless desirable to remove the obnoxious gases from a carrier air stream to such an extent that the scrubbed air can be exhausted into the space within the industrial building structure. This is especially important in geographical locations where atmospheric temperatures may deviate greatly from temperatures maintained within the industrial buildings since air exhausted to the atmosphere must be replaced by air coming in from outside of the building which air must then be heated or cooled as required to maintain the desired interior temperatures. Thus, substantial energy and costs may be saved by treating the polluted air to a degree sufficient to render interior exhausting permissible.
Air scrubbing towers are well known and generally include a body comprised of pieces or forms of inert solid material, usually referred to as the "pack" or "fill" which provides very large surface areas kept wet by scrubbing solution which is sprayed downwardly upon the pack as the air is passed upwardly, passing over the wet surfaces for reaction of the contaminant gases with the scrubbing liquid whereafter the air passes through a demister and is discharged from the tower at its top. Provision is made for a liquid sump at the bottom of the tower from which scrubbing liquid is drawn for recirculation by means of a pump to the sprayers and thence again downwardly through the pack. Means must be provided for replenishing water evaporated from the scrubbing solution and to maintain the effective and otherwise optimum acid composition of the solution. These solution servicing functions may be manual, but, in accordance with the invention herein described, both the provision of make-up water and the maintenance of the concentration of the scrubbing solution are fully automatic.
As an example of an industry which presents very serious problems of air pollution, reference may be made to the metal casting industry, especially the shell and core mold making operations which generate very offensive odors but also the casting operations, themselves, which also create polluting gases. The principal foundry air contaminants include triethyl amine, dimethylethyl amine, carbon dioxide, ammonia, formaldehyde, phenols, hydrogen cyanide and other materials in trace quantities. The odoriferous and noxious gaseous contaminants are removed by reaction with sulfuric acid as the air stream carrying the same passes through the scrubbing tower provided with pack continuously wetted by sulfuric acid solution. For maximum cleansing of the air, a tower comprising two, or even more, pack treatment bodies in series may be employed. As noted above, the additional cost of such series treatments can be justified by the savings realizable by discharging the scrubbed air inside of the foundry building.
The principal object of the invention is to provide an air scrubbing tower system wherein gaseous pollutants carried by the air are removed by acid scrubbing solution which solution is automatically maintained at the predetermined level or range of concentration for optimum operation and results. A further object is to provide such a tower system wherein the acid concentration is controlled by a control system which senses the conductivity of the scrubbing solution to effect the feeding of additional acid as required.
A further object is to provide alarms activated at predetermined maximum and minimum levels of concentration of the acid solution to call for manual rectification of a malfunction.
More specifically, an object of the invention is to provide a fully automatic acid scrubbing tower for air-polluting by-products generated in the various operations of the metal casting industry to remove the pollutant gases to such a degree that the treated air may be discharged from the tower interiorly of the building structure.